The present invention relates to a method and apparatus for the field rearing of planktonic larval forms of marine animals. This method and apparatus has particular application to fish and decapod crustaceans.
Over the past century, considerable effort has been expanded in attempts to rear marine larvae in the laboratory, but such methods have had very little success in rearing such larvae past the metamorphosis stage. The greatest difficulties with laboratory rearing have been in the collection and maintenance of wild plankton, or the laboratory culture of microplankton, used as food, and in maintenance of proper sanitation conditions within culture chambers. Such laboratory methods, moreover, have required unacceptably large amounts of time and labour making them impracticable for commercial use. Other problems in laboratory rearing of larvae include the difficulty in establishing proper lighting conditions, destruction of food plankton by pump impellors used to circulate unfiltered seawater systems and establishment of a proper seawater flow pattern to maintain the plankton in proximity to the larvae.
As a consequence of the aforementioned difficulties in the laboratory rearing of marine larvae, some attempts have been made to develop field rearing methods. Geoffrey Lawrence, at the 1978 Conference of the American Society of Limnology and Oceanography held in Victoria, British Columbia, Canada, described a screened cylindrical chamber employed in oceanic tidal water, whereby the water was allowed to simply flow straight through the chamber which contained flat fish larvae. No feature was present in the latter method to accumulate food plankton or to maintain the food plankton in close proximity to the larvae. The latter method also failed to provide a self-operating mechanism for withdrawing waste material from the tank. Consequently, the Lawrence method was limited to rearing relatively small concentrations of larvae in numbers insufficient for a commercial operation.